Context-dependent olfactory learning monitored by activities of salivary neurons in cockroaches

Abstract

Context-dependent discrimination learning, a sophisticated form of nonelemental associative learning, has been found in many animals, including insects. The major purpose of this research is to establish a method for monitoring this form of nonelemental learning in rigidly restrained insects for investigation of underlying neural mechanisms. We report context-dependent olfactory learning (occasion-setting problem solving) of salivation, which can be monitored as activity changes of salivary neurons in immobilized cockroaches, Periplaneta americana. A group of cockroaches was trained to associate peppermint odor (conditioned stimulus, CS) with sucrose solution reward (unconditioned stimulus, US) while vanilla odor was presented alone without pairing with the US under a flickering light condition (1.0 Hz) and also trained to associate vanilla odor with sucrose reward while peppermint odor was presented alone under a steady light condition. After training, the responses of salivary neurons to the rewarded peppermint odor were significantly greater than those to the unrewarded vanilla odor under steady illumination and those to the rewarded vanilla odor was significantly greater than those to the unrewarded peppermint odor in the presence of flickering light.Similar context-dependent responses were observed in another group of cockroaches trained with the opposite stimulus arrangement. This study demonstrates context-dependent olfactory learning of salivation for the first time in any vertebrate and invertebrate species, which can be monitored by activity changes of salivary neurons in restrained cockroaches.

Cockroach GABAB receptor subtypes: Molecular characterization, pharmacological properties and tissue distribution

“…The knowledge of the molecular identity and the pharmacological properties of GB should now enable us to investigate these functions in detail, especially since various behavioral tests including learning paradigms (Watanabe et al, 2003;Kwon et al, 2004;Lent and Kwon, 2004;Watanabe and Mizunami, 2007;Matsumoto et al, 2012) have recently been established for P. americana.…”

Participation of NO signaling in formation of long-term memory in salivary conditioning of the cockroach

“…Drinking water and sugar-free yeast extract were provided ad libitum. The preparation for extracellular recordings from salivary neurons was described previously [10,27]. In short, individual animals were immobilized ventral side up on a paraffin plate.…”

“…Salivary neurons exhibit spontaneous spike activities [10,[27][28][29][30]. Responses of salivary neurons to peppermint or vanilla odor (R) were measured as relative increase of the spike frequency from the spontaneous level, i.e., (Rs-Ro)/Ro, where Rs or Ro is the summed spike frequency of two salivary neurons during a 2-s period of odor stimulation or that during a 2-s period before the onset of odor stimulation, respectively [10].…”

“…It is zero when there is no change of spike frequency by odor stimulation. Responses of salivary neurons to vanilla odor and peppermint odor did not differ before conditioning [10,27,29,30]. In all experiments, animals were divided into two groups: one group in which peppermint odor was used as CS+ and vanilla odor was used as CS-and one group that received conditioning with the opposite stimulus contingency.…”

“…In all experiments, animals were divided into two groups: one group in which peppermint odor was used as CS+ and vanilla odor was used as CS-and one group that received conditioning with the opposite stimulus contingency. Since we observed no statistical difference in the conditioning effect between these two groups [10,27,29,30], data from these two groups were pooled. The effect of conditioning was evaluated by comparing responses to CS+ and CS-using the Wilcoxon's test [10].…”